Hollow glass microspheres (HGMs) are well known in the art. Microspheres are widely used as fillers in the plastics industry and may be made as either solid or hollow microspheres. Hollow and solid microspheres are used in reflective paints, coatings, and are incorporated into molded plastic products to improve workability of a material or to provide improved finish or surface qualities of a material such as an extruded plastic product.
The formation of hollow glass microspheres (HGMs) is well known in the art. The production of hollow glass microspheres has been described in U.S. Pat. Nos. 3,365,315 (Beck); 4,661,137 (Gamier); 5,256,180 (Garnier); and 5,534,348 (Miller et al) and which are incorporated herein by reference. Further, it is known that certain latent blowing agents may be included in a fine glass powder, such blowing agents including sulfates such as alkali sulfate along with various hydrates, carbonates, and halides. The selection and use of such blowing agents are well known in the art. The latent blowing agents cause a single bubble to nucleate within each particle of glass exposed to high temperatures such as in a flame.
It is also known in the art to produce large macrospheres having hollow glass walls which provide a semipermeable liquid separation medium for containing absorbents. The production of macrosphere structures can be seen in reference to U.S. Pat. Nos. 5,397,759 and 5,225,123 to Torobin and which are incorporated herein by reference. The Torobin references disclose hollow glass macrospheres comprising multiple particle glass walls. The reference teaches the use of the macrospheres for gas/liquid separation and for use with absorbents but does not discuss any features or characteristics which would make the microspheres suitable as a hydrogen storage medium.
U.S. Pat. No. 4,842,620 (PPG Industries) is directed to non-crystalline silica fibers having porous walls which are used in gas separation. The fibers described in this application have different physical characteristics than microspheres and which makes fibers less desirable with respect to hydrogen separation and storage capabilities.
U.S. Pat. No. 6,358,532 (CaP Biotechnology, Inc.) uses porous-wall hollow glass microspheres for cell clustering and biomedical uses. The porous-wall structures are designed to readily release microsphere contents when present within a biotic system. Alternatively, the microspheres are used to provide a substrate to support cell growth within the porous-wall structure.
While the above references disclose a variety of glass microspheres and porous-wall structures, there remains room for improvement and variation within the art for providing an improved process and apparatus for forming a high yield of a homogenous population of HGMs.